The guiding hypotheses for this proposal are that enhancement of antigen (Ag) presentation through the interaction of Ag, antibody (Ab) and Fc receptors (FcR): 1) will stimulate active immunity to immunogens, and 2) will vary dependent on the type of FcR or the human Ab isotope involved. FcR-mediated uptake of Ag-Ab complexes can enhance Ag presentation by monocytes at least 100-fold. In addition, recent studies suggest that directing Ag to FcR in vivo may bring out substantial increases in the effectiveness of vaccines. Specific Aim 1 will be to determine which FcR types are most effective at enhancing Ag presentation by monocytes. This will be done by attaching Ag to (Fab')2 or Fab monoclonal Ab (mAb) specific for human FcgammaRI, FCgammaRII, FcgammaRIII (the FcR for IgG) or FcalphaR (the FcR for IgA). Assays will consist of varying numbers of Ag presenting cells, Ag-specific T cells, Ag alone, Ab alone or Ag-Ab conjugates. T cell proliferation and lymphokine production by T cells will be used to measure Ag presentation. Depending on the infectious agent or immunogen involved, the isotope of human Ab produced will vary. Specific Aim 2 will be to define the ability of all human IgG isotopes, and IgA, to participate in enhanced Ag presentation. The hapten NP will be linked to the Ag. Human Fc mouse Fab anti-NP chimeric Ab will be used to create Ag-Ab complexes. Chimeric Ab composed of each of the human IgG isotopes is available and the ratio of NP to Ag will be varied to vary the size of the complex. FcR type- specific mAb will be used as blocking agents to confirm which FcR are being utilized during FcR-enhanced Ag presentation. Human monocytes, macrophages and B cells all express one or more forms of FcR. In addition, B cells have surface immunoglobulin (Ig) which binds Ag and thereby also enhances Ag uptake and subsequent presentation. Dendritic cells are considered to be an important Ag presenting cell as well, although they do not appear to express FcgammaR on their surface. Specific Aim 3 will be to compare the efficiency of receptor-enhanced and non-enhanced Ag presentation among these cell types. These studies will not only improve our understanding of the normal immune response, but will also provide novel approaches for enhancing the effectiveness of vaccines.